normally it fluctuates much, especially if you have just a low number of clicks, however if you have more than 100 clicks i suggest you to start to filter the ads that appear on your site.
all depends on the ads that are being displayed... if there are no high paying ads in the queue, then the low money ads get displayed... you don't like earning a penny per click?
June seem to be a big contrast for me. My last day of May was above $100 but less than $50 for June so far.